Method of bonding metallic members by plastic-flow bonding and plastic-flow bonded body

ABSTRACT

The disclosure is concerned with a bonding method for bonding metallic members, which comprises the steps of: fitting a metallic members to another metallic member, followed by effecting preliminarily plastic bonding by means of a preliminarily bonding punch; and generating compression force in an axial direction of the members in the vicinity of the fitting portion of the bonding members after the preliminarily plastic bonding, and allowing part of the material of the bonding member to effect plastic-flow in such a manner as to fill a gap defined between the metallic members, so as to plastically bond the members; whereby the members are tightly integrated with each other.

This application is a divisional application of Ser. No. 10/677,291filed Oct. 3, 2003.

DETAILED DESCRIPTION OF THE INVENTION

1. Technical Field to Which the Invention Pertains

The present invention relates to a method of bonding metallic members byplastic-flow bonding, and a bonded body obtained by the method.

2. Related Art

Conventional methods for fitting metallic members to each other andsubjecting them by plastic-flow bonding include a method for subjectingtwo members to plastic-flow bonding in a gap-fitting state (for example,refer to Japanese Patent Laid-open No. 11-120743, page 4 and FIGS. 3 and4).

Furthermore, another method for fitting two metallic members to eachother includes a method of subjecting them to plastic-flow bonding in apress-fitting state (for example, refer to Japanese Patent Laid-open No.2001-54268, page 2 and FIG. 1).

In a bonding method disclosed in Patent Laid-open No.11-120743, sinceplastic-flow bonding is performed after metallic members are free-fittedwith a gap to each other, a portion other than the vicinity of a portionwhich is pressed to effect plastic-flow forms a gap, as a matter offact, which leads to relatively weak bonding strength, especially,bending strength. In particular, a problem will arise in the case wherethin metal plate members are pressed to effect plastic-flow for bonding.

In a bonding method disclosed in Japanese Patent Laid-open No.2001-54268, since plastic-flow bonding is performed after two membersare press-fitted to each other, there is no gap at a portion other thanthe vicinity of a portion which is pressed to effect plastic-flow, andtherefore, high bonding strength, in particular, high bending strengthcan be achieved. However, a scrape or a gall tends to occur in the twomembers at the time of the press-fitting, thereby bringing aboutoccurrence of bending due to the press-fitting or contamination.Moreover, high precision in shape of the bonding members is needed tomanage a press-fitting margin, thereby increasing a cost.

SUMMARY OF THE INVENTION

An object of the present invention is to provide, at a low cost, amethod for plastic-flow bonding with high bonding strength and highaccuracy, which eliminates any occurrence of contamination.

The present invention provides a method of bonding metallic members by aplastic flow bonding to produce a bonded body with an increased bondingstrength and free from contamination.

The present invention further provides a plastic flow bonded metallicbody with a high bonding strength and free of contamination. The bondedbody can be applied especially to an apparatus for rotating a rotatingdisc and a rotating shaft, the members being bonded to each other.

The present invention provides a bonding method for bonding metallicmembers, which comprises the steps of: fitting a metallic members toanother metallic member, followed by effecting preliminarily plasticbonding by means of a preliminarily bonding punch; and generatingcompression force in an axial direction of the members in the vicinityof the fitting portion of the bonding members after the preliminarilyplastic bonding, and allowing part of the material of the bondingmembers to effect plastic-flow in such a manner as to fill a gap definedbetween the metallic members, so as to plastically bond the members;whereby the members are tightly integrated with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general plane view of a hard disk drive to which the presentinvention is applied.

FIG. 2 is a vertical cross-sectional view of the hard disk drive shownin FIG. 1.

FIG. 3 is an enlarged cross-sectional view of a dynamic pressure bearingspindle motor, using a bonded body of a hub and a shaft, in the harddisk drive shown in FIG. 2.

FIG. 4 is a vertical cross-sectional view of the bonded body of the huband the shaft.

FIG. 5 is a side view of the shaft.

FIG. 6 is a vertical cross-sectional view of the hub.

FIG. 7 is a vertical cross-sectional view of a molding die used in aprocess of preliminarily plastic bonding.

FIG. 8 is an enlarged vertical cross-sectional view of a bonded portionof the shaft and the hub after completion of the preliminarily plasticbonding.

FIG. 9 is a vertical cross-sectional view of a molding die used in aprocess of plastic-flow bonding.

FIG. 10 is an enlarged vertical cross-sectional view of the bondedportion of the shaft and the hub after the completion of theplastic-flow bonding.

FIG. 11 is an enlarged vertical cross-sectional view of a groove of theshaft.

FIG. 12 is an enlarged vertical cross-sectional view of a round grooveof the shaft.

FIG. 13 is an enlarged view showing a groove having a knurl at theshaft.

FIG. 14 is an enlarged vertical cross-sectional view of the bondedportion of the shaft and the hub, representing a stress after thecompletion of the preliminarily plastic bonding.

FIG. 15 is an enlarged vertical cross-sectional view of the bondedportion of the shaft and the hub, representing a stress after thecompletion of the plastic bonding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is applied to a bonding method for bonding abonding member to a member to be bonded, which are used for a device forrotating the bonding member serving as a rotary disk and the member tobe bonded serving as a rotary shaft integrally connected to each other.

The method comprises the steps of:

inserting the member to be bonded into a fitting hole formed in thebonding member having an inner diameter greater than an outer diameterof the member to be bonded, followed by positioning the member to bebonded;

pressurizing a portion, in the vicinity of the fitting portion of themember to be bonded, of the bonding member at a load for generating astress enough to effect plastically deform the material of the bondingmember, followed by preliminarily plastic bonding;

further pressurizing the portion, in the vicinity of the fitting portionof the member to be bonded, of the bonding member at a load in excess ofan elastic limit of the material of the bonding member; and

generating compression force in an axial direction of the member to bebonded at the portion in the vicinity of the fitting portion of thebonding member, and then,

allowing part of the material of the fitting portion in excess of theelastic limit to effect plastic-flow in such a manner as to fill a gapdefined between the member to be bonded and the bonding member;

whereby the bonding member and the member to be bonded are tightlyintegrated with each other.

The present invention is also applied to a bonded body comprising abonding member and a member to be bonded, which are used in a device forrotating the bonding member on which rotary disks are stacked and themember to be bonding serving as a rotary shaft in integral bonding:

wherein a portion, in the vicinity of the fitting portion of the memberto be bonded, of the bonding member is pressurized at a load forgenerating a stress enough to plastically deform the material of thebonding member, followed by preliminarily plastic bonding;

further the portion, in the vicinity of the fitting portion of themember to be bonded, of the bonding member is pressurized at a load inexcess of an elastic limit of the material of the bonding member; and

a compression force in an axial direction of the to-be-bonded member isgenerated at the portion in the vicinity of the fitting portion of thebonding member, and then, part of the material of the fitting portion inexcess of the elastic limit is allowed to plastic-flow in such a manneras to fill a clearance defined between the member to be bonded and thebonding member;

whereby the bonding member and the member to be bonded are tightlyintegrated with each other.

The present invention is further applied to a mechanical apparatusprovided with a bonded body comprising a bonding member and a member tobe bonded, which are used in a device for rotating the bonding member onwhich rotary disks are stacked and the to-be-bonded member serving as arotary shaft in integral bonding:

wherein a portion, in the vicinity of the fitting portion of theto-be-bonded member, of the bonding member is pressed to provide aplastically deformed part, which is in the vicinity of the fittingportion of the to-be-bonded member and is further pressed, followed byplastic-flow bonding.

The technical fields to which the present invention is applied are abonding method for subjecting, to plastic-flow bonding, metallic memberssuch as a shaft and a hub in a spindle motor for use in a disk device, aDVD or a CD-ROM in a computer or the like, in particular, in a spindlemotor having a dynamic pressure bearing structure, which is a thin-typehard disk drive motor to be loaded in a portable personal computer suchas a notebook personal computer. In addition, it relates to a bondedbody with reference to FIGS. 1 to 15. For the convenience, there are setforth meanings of all reference numerals in the following table. TABLE 1Shaft 2 Hub 3 Disc 4 Disc spacer 5 Clamp 6 Screw 7 Housing 8 Dynamicpressure bearing metal 10 Thrust receiving plate 11 Base 12 Stopper ring13 Magnet 14 Stator core 21 Bonding hole 22 Edge portion 23 Bottom face25 Outer diameter of hub 24 Flange 31 Annular groove 32 Female screw 34Edge portion 40 Spherical edge portion 41 Thrust receiving face 42Stopper groove 60 Preliminary bonding punch 61 Guide ring 62 Innerdiameter 63 Stand 64 Guide hole 65 Inner diameter of guide ring 66Preliminary bonding projection 67 Screw hole 70 Punch 71 Preliminarybonding mark 72 Bottom portion of preliminary mark 74 Guide hole 76Bonding projection 80 Preliminary bonded body 100 Dynamic pressurebearing spindle motor 200 Hard disc 300 Read-out device

The bonding method for subjecting the two members to the plastic-flowbonding and the bonded body according to the present invention areexemplified here in a dynamic pressure bearing spindle motor in a harddisk drive by the use of a bonded body including a hub and a shaft in apreferred embodiment.

FIG. 1 is a general plane view of a hard disk drive, and FIG. 2 is across-sectional view of the hard disk drive shown in FIG. 1.

In FIGS. 1 and 2, reference numeral 200 designates a hard disk of a harddisc drive (abbreviated as “an HDD”), in which a dynamic pressurebearing spindle motor 100 is disposed. A read-out device 300 reads outdata from a hard disk rotationally driven by the dynamic pressurebearing spindle motor 100.

FIG. 3 shows a dynamic pressure-bearing spindle motor in the hard diskdrive, in which a bonded body of a hub and a shaft is used, in apreferred embodiment according to the present invention.

In FIG. 3, a shaft 1 is integrated with a hub 2 by a bonding methodaccording to the present invention. To the hub 2 is securely fixed amagnet 13. A plurality of disks 3 serving as storage mediums are stackedon a flange 24 of the hub with disk spacers 4 held therebetween and aresecured by a clamp 5 that is tightened to a female screw 32 of the shaft1 with a screw 6. The shaft 1 is rotatably fitted into the bore of adynamic pressure bearing metal 8 secured to a housing 7. Thus, a radialdynamic pressure bearing is constituted by the effect of a dynamicpressure generated by a magnetic fluid filled inside the housingaccording to rotation. The housing 7 is fixedly secured to a base 11. Athrust receiving plate 10 is joined to the housing 7 while a stopperring 12 is held between the dynamic pressure bearing metal 8 and thethrust receiving plate 10, and thus, constitutes a thrust bearing inwhich a spherical edge portion 40 of the shaft 1 is supported at athrust receiving face 41. The shaft 1 is suppressed by the stopper ring12 fitted into a stopper groove 42 from floating in a thrust direction.A wound stator core 14 is securely bonded to the base 11 with anadhesive, and therefore, the magnet 13 receives rotating force at thetime of energization, thereby rotating the hub 2.

Next, an explanation will below be made of the hub 2 and the shaft 1. Itis desirable that the hub 2 as a bonding member should be made of amaterial which is liable to plastically deform and has deformationresistance is smaller than that of the shaft 1 serving as a member to bebonded. The hub 2 is made of ferrite stainless steel, for example,SUS430 in consideration of corrosion resistance and magneticcharacteristics in terms of a motor. The shaft 1 is formed into acolumnar shape, and is made of martensitic stainless steel excellent inabrasion resistance or corrosion resistance such as SUS440 or SUS420 J2in consideration of bearing performance, followed by hardening. At anouter diameter portion to be bonded in the vicinity of one end of theshaft 1 is formed an annular groove 31. The details of the shape of thegroove will be described later.

FIG. 4 shows a bonded body of the hub and the shaft in a preferredembodiment according to the present invention. In FIG. 4, the shaft 1 isprovided with the annular groove 31 formed in the outer diameter portionto be bonded in the vicinity of one end of the shaft 1 and isplastically bonded to a bonding hole 21 formed in the hub 2 having adiameter greater than the outer diameter of the shaft 1 by a method,described below, as shown in FIG. 6. The shaft 1 and the hub 2 arebonded to each other through a first process in which the shaft 1 shownin FIG. 5 is freely fitted or gap-fitted to the hub 2 shown in FIG. 6,followed by preliminarily plastic bonding, and a second process ofplastic-flow bonding.

First, a description of the first process of the preliminarily plasticbonding will be given below. A bottom face 23 of the hub 2 is held by astand 63, as shown in FIG. 7. The hub 2 is held at an outer diameter 25thereof by an inner diameter 62 of a guide ring 61. Thereafter, an edgeportion 34 on a side on which the annular groove 31 is formed at theouter diameter portion to be bonded of the shaft 1 is inserted into andfitted to the bonding hole 21 of the hub 2.

It is desirable from the viewpoint of bonding accuracy that a clearanceor gap at the fitting portion between the shaft 1 and the hub 2 when theedge portion 34 of the shaft 1 is inserted into the bonding hole 21 ofthe hub 2, that is, a clearance between the wall surface of the bondinghole 21 of the hub 2 and the outer peripheral surface of the shaft 1should be set as small as 0 to 0.02 mm. In the present preferredembodiment, the outer diameter of the shaft 1 is set to 3.00 mm whilethe inner diameter of the bonding hole 21 of the hub 2 is set to 3.01mm.

In this manner, while the bottom surface 23 of the hub 2 is held by thestand 63, the edge portion 34 of the shaft 1 is inserted into and fittedto the bonding hole 21 of the hub 2. Thus, a preliminarily bonding punch60 is fitted to the inner circumference 65 of the guide ring 61 and theshaft 1 is fitted into a guide hole 64 formed at substantially thecenter of the preliminarily bonding punch 60, thereby holding the shaft1. The shaft 1 is held in the guide hole 64 of the preliminarily bondingpunch 60 guided on the inner circumference 65 of the guide ring 61, andthen, the preliminarily bonding punch 60 is driven by a press ram, notshown into the bonding member. When the preliminarily bonding punch 60is driven by the press ram, a ring-like projection 66 having aprojection width K is formed at the tip of the preliminarily bondingpunch 60 by which an edge portion 22 of the hub 2 is pressed down in thevicinity of the bonding hole 21.

The pressing force of the preliminarily bonding punch 60 is a load thatgenerates stress large enough to plastic-deform the material forming thehub 2, and force that plastically deforms a portion corresponding tosuch a depth as to fill the fitting clearance between the shaft 1 andthe hub 2 vertically. The preliminarily bonding punch 60 is pressed downat the above-described load, and then, the material in the vicinity ofthe bonding hole 21 of the hub 2 is allowed to plastic-flow, followed bythe preliminary bonding. The bonding portion after the preliminarilyplastic bonding in the above-described manner is shown in FIG. 8, whichis an enlarged vertical cross-sectional view.

Subsequently, an explanation will below be made of the second process ofthe plastic-flow bonding. In the second process shown in FIG. 9, apreliminary bonded body 80 of the shaft 1 and the hub 2 which have beensubjected to the preliminarily plastic bonding is held by the stand 63at the bottom face 23 of the hub 2, and the outer diameter 25 of the hub2 is held by the inner diameter 62 of the guide ring 61. Then, the shaft1 is held in a guide hole 74 formed in a punch 70 guided on the innerdiameter 65 of the guide ring 61. In this state, a press ram, not shown,drives the punch 70 into the bonding member. When the punch 70 is driveninto the bonding member, a ring-like bonding projection 76 presses aportion of the bottom portion 72 of a preliminarily bonding mark 71 inthe vicinity of the bonding hole 21. The ring-like bonding projection 76is disposed at the tip of the punch 70 and has a projection width Wsmaller than the projection width K of the preliminarily bondingprojection 66 of the preliminarily bonding punch 60.

The pressing force of the punch 70 is a load large enough to generate astress for effecting a plastic deformation of the material forming thehub 2. The punch 70 is pressed down at the above-described load, andthen, the material in the vicinity of the bonding hole 21 of the hub 2is allowed to effect plastic-flow over the entire circumference of thegroove 31, followed by the bonding. The bonded portion after theplastic-flow bonding in the above-described manner is shown in FIG. 10,which is an enlarged vertical cross-sectional view of the bonding.

Furthermore, in order to achieve a high bonding accuracy, the smallerthe gap between the guide hole 64 of the preliminarily bonding punch 60or the guide hole 74 of the punch 70 and the outer peripheral surface ofthe shaft 1, the higher the bonding accuracy is obtained. Moreover, ifthe projecting width K and pressing depth J due to the preliminarilybonding projection 66 of the preliminarily bonding punch 60 are toolarge, the load for effecting the plastic deformation becomes large,thereby degrading the accuracy of the hub 2.

Additionally, if the projecting width W and pressing depth H due to thebonding projection 76 of the punch 70 are too great, the load for theplastic deformation becomes large, and therefore, the material more thanthat flowing in the groove is liable to be fluidized, thereby degradingthe bonding accuracy. Thus, the projecting width W and the pressingdepth H are set according to the shape of the groove.

Next, a description will be given below of the shape of the groove 31 ofthe shaft 1. FIG. 11 shows one example of the portion of the groove 31of the shaft 1. Factors determining the cross-sectional shape of thegroove 31 of the shaft 1 include the groove depth H, a groove width B, agroove angle θ, the number n of grooves and the like.

If the depth H of the groove 31 of the shaft 1 is too small, asufficient shearing strength cannot be achieved due to easy plasticdeformation when external force is exerted in an axial direction. Incontrast, if the depth H of the groove 31 of the shaft 1 is too large,the material insufficiently flows into the groove, thereby forming agap, so as to degrade the strength. As shown in FIG. 7, the screw hole67 for screwing the clamp 5 is formed at the lower portion of the shaft1, and further, the female screw 32 is disposed at the inner wallsurface of the screw hole 67 of the shaft 1. Consequently, the thicknessat a portion near the bonded portion of the hub 2 to the lower portionof the shaft 1 becomes small. Therefore, if the depth H of the groove 31of the shaft 1 shown in FIG. 11 is increased, the strength of the shaft1 is degraded. Thus, the groove depth H of the groove 31 of the shaft 1should desirably range from about 0.07 to about 0.13 mm.

The width B of the groove 31 of the shaft 1 can be varied according tothe shearing strength required at the bonded portion. However, if thewidth is set too largely, a distance from the tip of the punch 70 to thelower portion of the groove 31 of the shaft 1 becomes great in bondingto the hub 2, thereby increasing a fluid frictional loss of the materialin the vicinity of the bonding hole 21 of the hub 2, which should flowinto the groove 31 of the shaft 1. Therefore, even if the large load isapplied to the hub 2 by the punch 70, the internal stress of thematerial in the vicinity of the bonding hole 21 of the hub 2 near thelower portion of the shaft 1 cannot be increased enough to achieve theplastic deformation. As a consequence, the material in the vicinity ofthe bonding hole 21 of the hub 2 near the lower portion of the shaft 1is reduced in quantity of the plastic deformation, so that the materialin the vicinity of the bonding hole 21 of the hub 2 insufficiently flowsinto the groove 31 of the shaft 1. In this manner, if the depth H of thegroove 31 of the shaft 1 shown in FIG. 11 is increased, the strength ofthe shaft 1 is degraded. Thus, the depth H of the groove 31 of the shaft1 should desirably range from about 0.07 to about 0.13 mm.

Moreover, as shown in FIG. 11, as to the groove angle θ representing anopening degree (i.e., an angle) of the groove 31 of the shaft 1, if theopening angle θ of the groove 31 of the shaft 1 is small, the materialin the vicinity of the bonding hole 21 of the hub 2 is less prone toflow into the groove 31 of the shaft 1 when the large load is applied tothe hub 2 by the punch 70. In contrast, if the opening angle θ of thegroove 31 of the shaft 1 is great, the material in the vicinity of thebonding hole 21 of the hub 2 shallowly bites when the large load isapplied to the hub 2 by the punch 70, so that drawing strength becomessmall. In this manner, if the groove angle θ of the groove 31 of theshaft 1 shown in FIG. 11 is small, the material is less prone to flowinto the groove 31 of the shaft 1; in contrast, if the groove angle θ ofthe groove 31 of the shaft 1 is large, the drawing strength becomessmall. As a result, the groove angle θ of the groove 31 of the shaft 1should desirably range from about 60° to about 120°.

Furthermore, as the number n of grooves 31 of the shaft 1 is greater,the contact area between the shaft 1 and the hub 2 becomes larger,thereby increasing the drawing strength. However, if the number n ofgrooves 31 of the shaft 1 is great, the material in the vicinity of thebonding hole 21 of the hub 2 is less prone to flow into the groove 31 ofthe shaft 1 when the large load is applied to the hub 2 by the punch 70.As a consequence, if the number n of grooves 31 of the shaft 1 is toogreat, the drawing strength is much degraded. Thus, when the number n ofgrooves 31 of the shaft 1 is 2, the drawing strength is highest. Uponcomparison of the case of n=1 with the case of n=2 under the conditionthat the groove width B is the same, the contact area between the shaftand the hub is greater in the case of n=2, thereby increasing thedrawing strength.

Incidentally, the cross-sectional shape of the groove 31 of the shaft 1need not be a triangle as shown in FIG. 11. It may be a round shape, asshown in FIG. 12. In the case where a high torque strength is needed atthe bonded portion between the lower portion of the shaft 1 and the hub2, a knurl 36 may be formed at a thread between the grooves 31 of theshaft 1, as shown in FIG. 13.

Additionally, if the groove 31 of the shaft 1 is formed over the entirecircumference of the shaft 1, the material in the vicinity of thebonding hole 21 of the hub 2 plastically flows over the entirecircumference in a uniform manner when the large load is applied to thehub 2 by the punch 70, and further, strain also uniformly is exertedover the entire circumference, so that both of accuracy of a right angleand strength can be enhanced. In addition, the groove 31 of the shaft 1can be molded by lathing, thus achieving high productivity.

Furthermore, it is preferable that the position of the groove 31 of theshaft 1 should be set near a pressing surface 24 of the hub 2 aspossible. If the position of the groove 31 of the shaft 1 is positionedapart from the pressing surface 24 of the hub 2, a fluid frictionalresistance becomes high, and therefore, the material in the vicinity ofthe bonding hole 21 of the hub 2 is prone to flow into the groove 31 ofthe shaft 1.

In view of this, in the present preferred embodiment, as shown in FIG.14, the outer circumferential portion of the shaft 1 having the annulargroove 31 formed at the outer periphery of the shaft 1 is freely fittedinto the bonding hole 21 of the hub 2; the large load is applied to thehub 2 by the punch 70; the vicinity of the hole formed at the endsurface of the hub 2 is plastically deformed over the entirecircumference; the shaft 1 and the bonding hole 21 of the hub 2 aresubjected to the preliminarily plastic bonding in such a manner as tofill the gap; the material in the vicinity of the bonding hole 21 at theend surface is plastically deformed over the entire circumference afterthe preliminarily plastic bonding of the hub 2 in the state in which astress a is exerted on the bonding hole 21 of the hub 2; a compressionstress is exerted on the shaft 1 in such a manner as to fill the groove31 of the shaft 1; and then, the material in the vicinity of the bondinghole 21 of the hub 2 is allowed to plastic-flow. The shearing force andstrain P of the material in the vicinity of the bonding hole 21 of thehub 2 and the stress σ caused by the preliminarily plastic bonding areexerted on a portion remote from the pressing portion, on which thestrain is hardly exerted, as shown in FIG. 15. Thus, the connectionstrength between the hub 2 and the shaft 1 is high.

Incidentally, the present invention is not limited to theabove-described preferred embodiment, but it can be applied to bondingbetween other members of various kinds of metals, for example, a shaft,a cylinder or the like and a flat plate.

According to the present invention, it is possible to achieve thesufficient strength and accuracy without any occurrence of bending orcontamination even in the case of the bonding between the thin hub andthe small-diameter shaft.

Moreover, the fitting accuracy before the bonding may be rough incomparison with the press-fitting, the high productivity can be achievedin inexpensive equipment, and further, the fabricating cost can bereduced.

1. A bonding method for bonding metallic members, which comprises thesteps of: fitting a metallic members to another metallic member,followed by effecting preliminarily plastic bonding by means of apreliminarily bonding punch; and generating compression force in anaxial direction of the members in the vicinity of the fitting portion ofthe bonding members after the preliminarily plastic bonding, and,allowing part of the material of the bonding member to effectplastic-flow in such a manner as to fill a gap defined between themetallic members, so as to plastically bond the members.
 2. A bondingmethod for bonding a bonding member onto a member to be bonded, whichare used in a device for rotating the bonding member serving as a rotarydisk and the to-be-bonded member serving as a rotary shaft in integralbonding, the bonding method comprising: a first step of fitting thebonding member to the member to be bonded, followed by preliminarilyplastic bonding by a preliminarily bonding punch; and a second step ofgenerating compression force in an axial direction of the to-be-bondedmember in the vicinity of the fitting portion of the bonding memberafter the preliminarily plastic bonding in the first step, and then,allowing part of the material of the bonding member to plastic-flow insuch a manner as to fill a clearance defined between the bonding memberand the member to be bonded, so as to plastically bond the bondingmember onto the member to be bonded; whereby the bonding member and themember to be bonded are tightly integrated with each other.
 3. A bondingmethod for bonding a bonding member onto a member to be bonded asclaimed in claim 2, wherein the bonding member and the member to bebonded are freely fitted to each other.
 4. A bonding method for bondinga bonding member onto a member to be bonded, which are used in a devicefor rotating the bonding member serving as a rotary disk and theto-be-bonded member serving as a rotary shaft in integral bonding, thebonding method comprising the steps of: inserting the member to bebonded into a fitting hole formed at the bonding member having an innerdiameter greater than an outer diameter of the member to be bonded, andpositioning the member to be bonded thereat; pressurizing a portion, inthe vicinity of the fitting portion of the member to be bonded, of thebonding member at a load for generating a stress enough to plasticallydeform the material of the bonding member, followed by preliminarilyplastic bonding; further pressurizing the portion, in the vicinity ofthe fitting portion of the member to be bonded, of the bonding member ata load in excess of an elastic limit of the material of the bondingmember; and generating compression force in an axial direction of theto-be-bonded member at the portion in the vicinity of the fittingportion of the bonding member, and then, allowing part of the materialof the fitting portion in excess of the elastic limit to plastic-flow insuch a manner as to fill a clearance defined between the member to bebonded and the bonding member; whereby the bonding member and the memberto be bonded are tightly integrated with each other.
 5. A bonding methodfor bonding a bonding member onto a member to be bonded as claimed inclaim 1, wherein an annular groove is formed at the fitting portion ofthe to-be-bonded member to the bonding member.
 6. A bonding method forbonding a bonding member onto a member to be bonded as claimed in claim5, wherein a knurl is formed at the annular groove formed at the fittingportion of the to-be-bonded member to the bonded member.